JP2000339750A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain stable reproducibility in either phase-changed state by successively laminating a first interface controlling layer, a recording layer phase- changed to an amorphous phase or a crystalline phase according to the power of irradiating light, a second interface controlling layer and a reflecting layer and setting the phase-changing rate of the recording layer at the interface of the first interface controlling layer side higher than that at the interface of the second interface controlling layer side. SOLUTION: A recording layer 14 is composed of chalcogenides e.g. GeTe, GeSbTe, InSeTlCo, InSbTe, etc. Among them, GeTe and GeSbTe are preferable because of their high stability in the amorphous state. A first interface controlling layer 13 consists of nitrides, oxides or carbides containing at least one of elements selected from an element group consisting of Al, Si, V, Mn, Fe, Zn, Ga, Cr, Ge, Y, Zr, Mo, Ba, Sb and Te. A second interface controlling layer 15 consists of Al, Si, Cr, Co, Ni, Cu, Ag, Zn, S, Ge, Ga, Y, Sb, W, Ta, Ti, In, and the like and has higher thermal conductivity and compressive stress than those of the first interface controlling layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording layer having an amorphous-crystalline phase which changes in accordance with the output of a light beam such as a laser beam to be irradiated. The present invention relates to a rewritable optical recording medium which records and reproduces digital information by utilizing a difference in reflectance of the optical recording medium.

[0002]

2. Description of the Related Art FIG. 2 shows a partial cross-sectional view of a conventional rewritable optical recording medium M utilizing a phase transition (hereinafter, referred to as a medium M). In the figure, 1 is a disk-shaped substrate made of resin such as polycarbonate, glass or the like, and 2 is ZnS-
A first transparent dielectric layer made of SiO ₂ or the like, 3 is a recording layer made of GeTe or the like and capable of changing a phase to an amorphous-crystalline two-state, 4 is a second transparent dielectric layer made of ZnS-SiO ₂ or the like Reference numerals 5 and 5 are reflection layers made of a material having a high reflectance such as Al.

In such a rewritable medium M, the recording layer 3 has a different light reflectivity between the crystalline state and the non-crystalline state. Generally, the crystalline state has a higher reflectivity. . The operating principle of the medium M is as follows. First, all the recording bits of the recording layer 3 are crystallized. That is, initialization is performed in a state where the reflectance is high.
For writing information, a laser beam pulse-modulated to two types of laser power is irradiated while rotating the medium M, and a recording layer is irradiated with a recording bit irradiated with a high-power (about 10 to 20 mW) laser beam. The material becomes higher than the melting points of the three materials, and is melted and rapidly cooled to become amorphous. On the other hand, medium output (5
A recording bit irradiated with a laser beam (about 10 mW) is heated to a crystallizable temperature range equal to or lower than the melting point and then cooled to a crystalline state.

[0004] The above-mentioned writing operation can be performed directly after the old information remains, and each recording bit changes to a state corresponding to the new information. That is, overwriting by overwriting (Over Write, hereinafter abbreviated as OW) is possible. Reproduction is performed by irradiating a low-output (about 1 to 2 mW) laser beam for reading to determine whether the phase is a crystalline phase having a high reflectivity or an amorphous phase having a low reflectivity. read.

The material of the recording layer 3 is Te, S
A chalcogenide of a material containing one element of e and S is suitable, and the chalcogenide has a feature that it easily becomes amorphous. Specifically, GeTe-based materials, GeSbT
e-based materials, InSeTlCo-based materials, InSbTe-based materials, and the like.

Conventionally, such a phase change type medium M has an interface control layer formed on both sides or one side in contact with the phase change type recording layer, and the interface control layer has a thickness of 1000
Standard free energy of formation at -400kJ / mol
Consists O ₂ oxide in the range of -800kJ / molO _2, in particular _{Cr 2 O 3, SiO 2,} Ta 2 O
₅ , TiO ₂ , V ₂ O ₃ , or a combination thereof, the interface control layer is made of a thermally stable oxide, and the recording layer is destroyed due to repetition of recording and erasing. Which have less tendency to occur (see Conventional Example 1: Japanese Patent Application Laid-Open No. 5-140883).

As a second conventional example, there is provided an interface control layer formed on both sides or one side in contact with the phase change type recording layer,
An oxide in which a main component of the interface control layer is a combination of a cation having an ionic radius of 1.0 ° or more and O ²⁻ ions, ie, Y, La, C
By using any one of e, Gd, Dy, and Th or a combination thereof, the interface control layer is made of a thermally stable oxide, so that the recording layer is broken by repeated recording and erasing. Difficult ones are known (conventional example 2: see JP-A-5-342632).

Further, as a third conventional example, information comprising a phase change type recording layer formed on a substrate and a dielectric protection layer formed on the recording layer and / or between the substrate and the recording layer. A recording medium, between the dielectric protective layer and the recording layer, a metal that has a higher melting point than the recording layer material and does not form a solid solution with the recording layer material,
A boundary layer made of an alloy or an intermetallic compound, wherein the boundary layer is made of W, Ta, Re, Ir, Os, Hf, Mo, Nb, R
u, Tc, Rh, Zr, alloys of two or more of these metals,
By using a material selected from the group consisting of Ta-W, W-Si, Mo-Si, and Nb-Al, the adhesion between the dielectric protective layer and the recording layer is improved, and information having excellent repetition characteristics is obtained. A recording medium is known (conventional example 3: see JP-A-7-262614).

As Conventional Example 4, a seed layer is provided adjacent to the phase-change type recording layer, which is composed of a mixed film in which metal particles are dispersed in a dielectric, and has an action of controlling the crystal grain size of the recording layer. Therefore, it is known that when a minute recording mark is formed, the disturbance of the mark edge is small and the jitter characteristic is good (conventional example 4: JP-A-10-1060).
No. 27).

[0010]

However, conventionally,
In the above-mentioned phase-change recording layer, it is necessary that both the crystalline phase and the amorphous phase be formed stably with good reproducibility and that the phase can be transferred at high speed. However, there is a problem that even if one of the crystalline phase and the amorphous phase is formed stably, the other is likely to be unstable.

Further, in the above-mentioned conventional examples 1 to 4, the interface control layer is formed on both sides or one side in contact with the phase-change type recording layer, so that the recording layer is less likely to be destroyed by repeated recording and erasing. The type and the type with improved jitter characteristics are of the same type between the interface control layers above and below the recording layer. That is, the thermal conditions on the upper and lower sides of the recording layer are the same. Further, in the conventional examples 1 to 4, there is no mention that the formation of one of the above-mentioned crystalline phase and amorphous phase is likely to be unstable.

Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a recording medium of the phase change type, which is used when the recording layer changes into two states, a crystalline phase and an amorphous phase. An object of the present invention is to stably form the two states with good reproducibility.

[0013]

The optical recording medium of the present invention comprises:
On a transparent substrate, a first interface control layer, a recording layer that changes to an amorphous or crystalline phase according to the output of irradiation light, a second interface control layer, and a reflective layer are sequentially laminated, and the recording layer The phase change speed at the first interface control layer side interface is higher than the phase change speed at the second interface control layer side interface.

According to the present invention, the crystal growth rate of the entire recording layer is increased by increasing the phase change speed at the interface on the first interface control layer side which is located on the light incident side of the recording layer and is easily heated. Can be improved. As a result, as in the case of the crystalline state, the phase changes quickly even when the state changes to the amorphous state, and the jitter characteristics, high-speed recording, and high-speed erasing characteristics at the recording bit end are improved. Further, the two states of the crystalline phase and the amorphous phase are easily formed stably, and the repetitive recording / erasing characteristics are improved.

In the present invention, preferably, the recording layer is made of a chalcogenide, and the first interface control layer is made of Al, Si, V, Mn, Fe, Zn, Ga, Cr, G
a nitride containing one or more of the element group A consisting of e, Y, Zr, Mo, Ba, Sb, and Te; an oxide containing one or more of the element group A; or one or more of the element group A And the second interface control layer is made of Al, Si, C
r, Co, Ni, Cu, Ag, Zn, S, Ge, Ga,
A nitride containing one or more of the element group B consisting of Y, Sb, W, Ta, Ti, and In, an oxide containing one or more of the element group B, or containing one or more of the element group B The first interface control layer is made of carbide, and the thermal conductivity of the first interface control layer is smaller than the thermal conductivity of the second interface control layer.

According to the present invention, the first interface control layer has a temperature rising characteristic and a cooling rate which are superior to those of the second interface control layer, and as a result, the phase at the interface of the recording layer on the first interface control layer side is improved. The change speed is improved.

It can be inferred that the difference in the phase change speed depends on the thermal conductivity and the stress of the first and second interface control layers. The smaller the thermal conductivity, the larger the phase change speed. When the compressive stress is large, the phase change rate is small, and as the compressive stress changes to the tensile stress, the phase change rate increases. Therefore, more preferably, when the stress remaining in the first interface control layer is set as a tensile stress, and the stress remaining in the second interface control layer is made more compressive than the tensile stress, the first interface control layer side interface Further increases the phase change speed.

[0018]

FIG. 1 shows a basic layer structure of a medium M1 according to the present invention. In the figure, 11 is a disk-shaped transparent substrate made of polycarbonate, polyolefin, epoxy resin, acrylic resin, glass, tempered glass having a resin layer formed on the surface, translucent ceramics, etc., and 12 is Zn
First transparent dielectric layer made of S-SiO ₂ or the like, 13 consists of the first interface control layer, phase change recording layer 14, the second interface control layer 15, 16 is ZnS-SiO ₂ or the like The second transparent dielectric layer 16 is a reflection layer made of Al or the like.

In the present invention, the recording layer 14 is made of GeTe,
Materials made of chalcogenides, such as GeSbTe, InSeTlCo, and InSbTe, are preferable. Among them, GeTe,
GeSbTe is preferable in that the number of rewrites is large, crystallization can be performed in a short time when crystallization is performed, and the stability of the amorphous state is high.

Further, when a Ge _a Sb _b Te _c, 5
at (atomic)% ≦ a ≦ 70 at% is preferable, and a <5 at%
In this case, the phase change speed is low, and when 70 at% <a, the amorphous state becomes unstable. 0 at% ≦ b ≦ 50 at% is preferable and 5 at%
When 0 at% <b, the amorphous state becomes unstable. 40at
% ≦ c ≦ 70 at% is good. When c <40 at%, the crystallization temperature is too high, and when 70 at% <c, the crystallization temperature is too high. The thickness of the recording layer 14 is 5 to 5.
50 nm is preferable, and if it is less than 5 nm, the difference in reflectance between the crystalline state and the amorphous state becomes small, and if it exceeds 50 nm, characteristic deterioration such as BER (Bit Error Rate) due to repeated recording and reproduction becomes large. More preferably, it is 10 to 40 nm.

The first and second transparent dielectric layers 12, 16
Are the recording layer 14 and the first and second interface control layers 13 and 15
And the material is Zn.
S-SiO ₂ , SiN-based material, SiON-based material, SiO
_{2, SiO, TiO 2, Al} 2 O 3, Y 2 O 3, Ta
N, AlN, ZnS, Sb ₂ S ₃ , SnSe ₂ , Sb ₂
Se ₃ , CeF ₃ , amorphous silicon (hereinafter referred to as a-Si), TiB ₂ , B ₄ C, B, C and the like are preferable.

In particular, ZnS-SiO ₂ is preferable, and this material has little change in characteristics at high temperatures. (ZnS) _x (Si
O ₂ ) When _100-x , 60 at% ≦ x ≦ 95 at%
Is preferable, and when x <60 at%, heat resistance is poor, and x>
At 95 at%, the particle size of ZnS becomes large and the jitter is deteriorated.

The reflection layer 16 is made of Al, A having a high reflectance.
1Cr alloy, AlCu alloy, AlTi alloy, Au, A
g, AuCu alloy, Pt, AuPt alloy and the like are preferably used.

The first interface control layer 13 of the present invention is made of Al, S
i, V, Mn, Fe, Zn, Ga, Cr, Ge, Y, Z
one of the element group A consisting of r, Mo, Ba, Sb, Te
It is preferable that the second interface control layer 15 be made of a nitride containing at least one species, an oxide containing one or more kinds of the element group A, or a carbide containing one or more kinds of the element group A. Compared with materials, thermal conductivity is small, compressive stress is small,
Alternatively, it has a characteristic of having a tensile stress. More preferably, the first interface control layer 13 is made of Al, Si, V, M
a nitride containing one or more of the element groups Aa consisting of n, Fe, Ga, Y, Zr, Mo, Ba, and Te; an oxide containing one or more of the element groups Aa; It may consist of a carbide containing more than one species.

As the first interface control layer 13, specifically, CrN, SiC, SiO, CoN, CrO.Ba
C, ZrC · TeC, AlO · SiN, ZnC · YO,
GaO, AlO-SiN-Cr, SiC-AlO, VO
-Mo, MnC, FeN, ZnC, GaO and the like.

The second interface control layer 15 is made of Al, Si, C
r, Co, Ni, Cu, Ag, Zn, S, Ge, Ga,
A nitride containing one or more of the element group B consisting of Y, Sb, W, Ta, Ti, and In, an oxide containing one or more of the element group B, or containing one or more of the element group B It may consist of carbides, these materials being the first interface control layer 13
As compared with the above, there is a characteristic that the thermal conductivity is large and the compressive stress is large. More preferably, the second interface control layer 15
Are Cr, Co, Ni, Cu, Ag, Zn, S, Ge, G
a, Sb, W, Ta, Ti, In containing at least one element from the element group Bb, oxide containing at least one element from the element group Bb, or containing at least one element from the element group Bb It is preferably made of carbide.

As the second interface control layer 15, specifically, SiN, AlN, AlN.Cr, Y.SiN, Ge
N-GaN, GeN, SiN-WC, CrN-CuN,
TiN • TaO, SiN • AlO, GeN • SiN, S
bN, CoN, NiON, AgN.In, ZnSO, and the like.

The first interface control layer 13 and the second interface control layer 15 are formed by a sputtering method using a single type of target or a composite target. A film can also be formed by performing reactive sputtering with a mixture of oxygen, oxygen and the like.

The thermal conductivity of the first interface control layer 13 is preferably smaller than the thermal conductivity of the second interface control layer 15. That is, (thermal conductivity of the first interface control layer 13)
The ratio of / (thermal conductivity of the second interface control layer 15) is preferably 0.7 or less, and in this case, the phase change rate is in the following preferable range. That is, in the present invention, the phase change speed at the interface of the recording layer 14 at the first interface control layer 13 side is 1.5 times or more higher than the phase change speed at the interface of the second interface control layer 15 side. It is preferable that the crystal growth rate of the entire recording layer 14 is increased by increasing the phase change rate at the interface on the first interface control layer 13 side which is located on the light incident side of the recording layer 14 and is easily heated. Extremely improved and rapid crystallization is achieved. The same applies to the case of amorphization. More preferably, the phase change speed at the interface of the recording layer 14 at the first interface control layer 13 side is 2.0 times or more higher than the phase change speed at the interface of the second interface control layer 15 side.

The phase change speed and the phase change speed ratio can be measured as follows. The entire recording layer 14 is made amorphous and irradiated with a laser beam to raise the temperature from the crystallization temperature to the melting point for 5 to 50 nsec. Then, the cross section of the cooled recording layer was examined by a transmission electron microscope (Transmission Electron Microscope).
Microscope: TEM), derive the areas of the crystalline phase and the amorphous phase from the image and use them as the respective phase change rates, and calculate the area ratio of the crystalline phase and the amorphous phase as the phase change rate ratio (in this case, (Crystallization rate ratio). Similarly, the amorphousization rate ratio can be measured by raising the temperature to the melting point or higher for 5 to 50 nsec.

Thus, in the optical recording medium of the present invention, the phase change speed in the entire recording layer is improved, and when the phase changes to the crystalline phase or the amorphous phase, the phase changes rapidly, and the jitter at the recording bit end is reduced. The characteristics, high-speed recording and high-speed erasing characteristics are improved, and the two states of the crystalline phase and the amorphous phase are each easily formed stably, and the effect of repeatedly recording and erasing is improved.

In the present invention, each of the above-mentioned layers is
2 each of which is laminated on both sides of the
By attaching two transparent substrates 11, the recording capacity may be doubled. The present invention is not limited to the light intensity modulation method for pulse-modulating a laser beam, but may be applied to a heating method using energy beams such as an electron beam and an electromagnetic wave. The medium M1 of the present invention is a rewritable optical disk, such as DVD (digital video disk), CD
(Compact disk) and optical disks such as CD-ROM.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0034]

Embodiments of the present invention will be described below.

Example 1 The medium M1 (optical disk) shown in FIG. 1 was constructed as follows. The following layers were sequentially formed on the main surface of a 3.5-inch disk-shaped transparent substrate 11 made of polycarbonate by magnetron sputtering.

A film thickness of about 1500 °, (ZnS) ₈₀ (SiO
₂ ) The first transparent dielectric layer 12 composed of ₂₀ ;
First interface control layer 13 made of various materials (Table 1), recording layer 1 made of Ge ₂ Sb ₂ Te ₅ and having a thickness of about 200 °
4. The second interface control layer 15 made of various materials (Table 1) having a thickness of about 100 °, a thickness of about 200 °, (ZnS) ₈₀ (Si
O ₂ ) _{20, a} second transparent dielectric layer 16 having a thickness of about 100
0 °, a reflective layer 17 made of an Al—Cr alloy.

Further, as Comparative Example 1, a layer having neither the first interface control layer 13 nor the second interface control layer 15 was prepared. As Comparative Example 2, a device having the same configuration as that of Example 1 except that the first interface control layer 13 was not provided and the second interface control layer 15 was made of SiN having a thickness of about 100 ° was manufactured. As Comparative Example 3, the first interface control layer 13 has a thickness of about 1
A structure was formed in the same manner as in Example 1 except that the second interface control layer 15 was not formed, except that the second interface control layer 15 was not formed. As Comparative Example 4, the first interface control layer 13 has a thickness of about 100
The second interface control layer 15 has a thickness of about 10
A structure similar to that of the first embodiment was produced except that it was made of SiN of 0 °.

For these, the crystallization rate ratio ｛(crystallized area per unit area at the interface on the first interface control layer 13 side in the cross-sectional TEM image) / (cross-sectional TEM image)
(Crystallized area per unit area at the interface on the second interface control layer 15 side in the image)｝, jitter characteristics (%) at the end of the recording bit when the track of the optical disc is reproduced at a linear velocity of 6 m / sec, Table 1 shows the measurement results of the OW erasing rate (dB) when recording and reproducing at a speed of 6 m / sec and the high-speed OW erasing rate (dB) when recording and reproducing at a linear velocity of 15 m / sec.

[0039]

[Table 1]

The OW erasure rate was measured as follows. First, set the linear velocity of the track on the optical disc to 6
m / sec or 15 m / sec, light wavelength 830 nm
Irradiates a laser beam pulse-modulated to 13 mW (corresponding to an amorphous state) and 5 mW (corresponding to a crystalline state),
Recording is performed at 4.91 MHz and a pulse width of 30 ns, then OW is performed at 1.84 MHz and a pulse width of 30 ns, and the carrier level at 4.91 MHz before the OW and 4.9 after the OW.
The difference in carrier level at 1 MHz was defined as the OW erasure rate.

As shown in Table 1, the product of the present invention had a jitter characteristic of 7.7% or less, an OW erasing rate of -29.5 dB or less, and a high-speed OW erasing rate of -23.3 dB or less. On the other hand, in Comparative Examples 1 to 3, the jitter characteristic was 1
The OW erasing rate deteriorated to 0.42% or more, the OW erasing rate to -27.7 dB or more, and the high-speed OW erasing rate to -12.4 dB or more. Comparative Example 4 had a jitter characteristic of 8.1% and an OW erase ratio of -3.
Although it was relatively good at 1.2 dB, the high-speed OW erasing rate was -15.3 dB, which was worse than that of the product of the present invention.

[0042]

According to the present invention, the phase change speed at the first interface control layer side interface of the recording layer is higher than the phase change speed at the second interface control layer side interface. The crystal growth rate is improved, and when the phase changes to a crystalline phase and an amorphous phase, the phase changes rapidly, and the jitter characteristic at the end of the recording bit,
The high-speed recording and high-speed erasing characteristics are improved, and both the crystalline phase and the amorphous phase are easily formed in a stable manner.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of an optical recording medium M1 of the present invention.

FIG. 2 is a partial cross-sectional view of a conventional optical recording medium M.

[Explanation of symbols]

 1: transparent substrate 2: first transparent dielectric layer 3: recording layer 4: second transparent dielectric layer 5: reflective layer 11: transparent substrate 12: first transparent dielectric layer 13: first interface control layer 14: Recording layer 15: Second interface control layer 16: Second transparent dielectric layer 17: Reflective layer

Claims (2)

[Claims] A first interface control layer, a recording layer that changes into an amorphous or crystalline phase in accordance with the output of irradiation light, a second interface control layer, and a reflective layer are sequentially laminated on a transparent substrate. An optical recording medium, wherein a phase change speed of the recording layer at a first interface control layer side interface is higher than a phase change speed at a second interface control layer side interface. 2. The recording layer comprises a chalcogenide, and the first interface control layer comprises Al, Si, V, Mn, Fe, Z.
n, Ga, Cr, Ge, Y, Zr, Mo, Ba, Sb,
The second interface control, which is made of a nitride containing one or more of the element group A made of Te, an oxide containing one or more of the element group A, or a carbide containing one or more of the element group A; The layers are Al, Si, Cr, Co, Ni, Cu, Ag, Z
n, S, Ge, Ga, Y, Sb, W, Ta, Ti, In
A nitride containing one or more of the element groups B, an oxide containing one or more of the element groups B, or 1 of the element group B
2. The optical recording according to claim 1, wherein the first interface control layer is made of a carbide containing at least one species, and the thermal conductivity of the first interface control layer is smaller than the thermal conductivity of the second interface control layer. Medium.